Separation of diolefins



Reissued Aug. 28, 1945 SEPARATION OF DIOLEFINS Rupert (J. Morris and Harry de V. Finch, Berkeley,

CaliL, assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Original No. 2,373,329, dated April 10, 1945, Serial No. 404,064, July 25, 1941. Ap- May 26, 1945, Serial No.

plication for reissue 596,090

9 Claims.

This invention relates to the separation of diolefins from hydrocarbon mixtures, and more particularly to the separation of isoprene and piperylene from mixtures which are rich in oleflns, such as those produced by the vapor-phase cracking of petroleum or petroleum fractions. In one of its more specific embodiments the invention pertains to the separation 01' isoprene and piperylene from hydrocarbon mixtures rich in olefins, these mixtures boiling substantially close to the boiling temperatures of these dioleflns so as to render their recovery by ordinary distillation processes impractical and in some cases substantially impossible. The invention is also directed to a novel compound described hereinbelow.

Both isoprene (2-methyl-butadiene-l,3) and piperylene (pentadiene-1,3) are valuable compounds which may be used for the manufacture of various intermediate, auxiliary and final products for the textile, resin; lacquer, dye-stuff and related industries. For example, both of these compounds are highly suitable for the preparation of products of polymerization. Also, the sul'fone derivatives of isoprene and piperylene can be used as intermediate for the manufacture of organic dye-stuffs and textile assistants, some of the reaction products formed from these sulfones being suitable as solvents and softeners.

It is known that hydrocarbon fractions, even when they boil within relatively narrow ranges, consist of a number of different hydrocarbons having difierent structures, possessing different properties and characteristics, and suitable for difierent uses. For example, when a hydrocarbon fraction formed by the pyrolysis of hydrocarbons of the type of naphtha, kerosene, stove oil, or the like, is fractionally distilled to recover separately the fraction boiling between about 25 C. and about 50 C. to 55" C., this narrow boiling fraction will predominate in various olefins having five carbon atoms per molecule. Besides the different amylenes (i.e. straight-chain or branched-chain mono-oleflns having five carbon atoms per-molecule) this fraction will also contain greater or lesser concentrations of isoprene g It has been previously proposed to separate diolefins from narrow-boiling, olefin-containing tion under a reduced pressure, to. recover the dicyclopentadiene as the bottom fraction, and depolymerizing the separated dicyclopentadiene, for example, by heating it at or near its boiling temperature in a still, preferably with provision for removing and condensing the cyclopentadiene vapors as rapidly as they are formed.

It is also known that acyclic dioleflns may be separated from oleflnic or olefin-containing mixtures by contacting such mixtures at elevated temperatures and pressures with sulfur dioxide to form the sulfones of these dioleflns. These sulfones are then separated from the unreacted hydrocarbons by cooling the reaction mixture to effeet the separation of the solid sulfones. The chief difiiculty'of this method lies in the fact that, unless suitable precautions are taken, instead of forming crystalline or crystallizable sulfones Which upon heating readily decompose to yield substantially quantitative amounts of the diolefins, a reaction between the acyclic diolefins and sulfur dioxide tends toward the formation of insoluble amorphous products which do not readily yield the dioleflns when subjected to ordinary processes of decomposition. The amorphous compounds are diolefin poly-sulfones, while the crystalline compounds are mono-sulfones, i. e. monomeric diolefln sulfones. In order to prevent the formation of the poly-sulfones, it has been previously proposed to effect the reaction in the presence of oxidation-inhibiting phenolic substances, such as hydroquinone, pyrogallol, pyrocat-echo], and the like, or by avoiding the presence of a large excess of the sulfur dioxide in am reaction zone.

In all cases of separation of the acyclic diolefins frorn hydrocarbon mixtures containing the same, the sulfones formed were separated as a solid crystalline and/or amorphous mass, depending on whether the reaction between the diolefins and the sulfur dioxide produced monomeric or polymeric sulfones, or mixtures thereof.

This separation was effected by cooling the reaction mixture substantially to room temperatures, recovering the solid sulfones for instance by filtration, and subsequently decomposing these sulfones to recover the diolefins. If the original hydrocarbon mixture thus treated contained more than one type of dioleflns, it was heretofore necessary to subject the diolefins thus recovered from the solid sulfones to a difficult fractionation to obtain the individual dioleflns. v

It has now been discovered that not all of the sulfones formed by the reaction of acyclic diolefins with sulfur dioxide are solid at or substantially near ordinary temperatures and pressures. It has been particularly found that, whereas the monomeric isoprene sulfone is a normally solid, white crystalline material which melts without decomposition at a temperature of about 64 C., monomeric piperylene sulfone isa normally liquid substance, the physical and chemical characteristics of which are totally different from thbse of the aforementioned monomeric isoprene sulfone.

In view of the aforementioned discovery, it was found that isoprene and piperylene maybe separately and readily recovered from hydrocarbon fractions containing the same, and especially from narrow-boiling fractions predominating in or substantially consisting of five-carbon atom unsaturated hydrocarbons, these acyclic diolefins being obtainable either as such or in the form of their monomeric sulfones. Broadly stated, this is accomplished by reacting the diolefin-containing hydrocarbon fraction with sulfur dioxide under conditions whereby the formation of the monomeric diolefin sulfones is favored, separating these sulfones from the reaction mixture and, after cooling to substantially room temperatures (1. e.

between about 15 C. and about 25C.) or below,

of the mentioned C acyclic diolefins, thus rendering their separation byordinary distillation highly difficult, if not totally impossible. On the other hand, since monomeric isoprene sulfone is readily crystallized (by cooling to a temperature below 64 C.), while the monomeric piperylene sulfone is normall liquid, it is possible to form these'sulfones by reacting the C5 fraction containing isoprene and piperylene with sulfur dioxide, recovering the sulfones cooling them to crystallize and separate the isoprene sulfone and then, if desired, decomposing the two sulfones separately, thereby recovering substantially quantitative yields of the acyclic diolefins.

It was also discovered that the rate of additionof sulfur dioxide to various acyclic diolefins, even those having the same number of carbon atoms per molecule, is not the same, For example, when an oleflnic fraction boiling between about 32 C. and about 36 C., and containing isoprene as to the only acyclic diolefl'n therein (this di olefin comprising about 44.3% by weight of the fraction), was treated for about 0.5 hour at a temperature of about 99 C; with sulfur dioxide employed in a 3.86:1 mol ratio, i. e. 3.86 mols of sulfurdiox ide per mol of isoprene, the yield of the solid monomeric isoprene sulfone was equal to about 95.5%. On the other hand, when the starting material consisting of an olefl nic hydrocarbon fraction boiling between-about 41 C. and about 44 C. and consisting of mono-oleflns and about 42.8 weight per cent of piperylene, the yield of the monomeric piperylene sulfone, when subiected to the same treatment; was only about 73.3%. In order to raise this yield to 96.3%, it was necessary to continue the heating for about 2 hours. Also, under similar operating conditions, it was necessary to heat a mixture of sulfur dioxide and a butadiene-containing olefinic fraction for about 2% hours before the monomeric butadlene sulfone yield was equal to 97.1%. Therefore, because of the mentioned difference in the rates of reaction between sulfur dioxide and a the various acyclic dioletlns, it is possible to obtain concentrated diolefin sulfones or to isolate individual sulfones by regulating the reaction tlme'and, if desired, the quantity of sulfur dioxide added.

According to the process of the present invention, in order to prevent or inhibit the formation of the amorphous insoluble poly-sulfones,- the hydrocarbon fraction, prior to its reaction with sulfur dioxide, is first treated to remove any organic peroxides which may be present therein. This is because the presence of the peroxides during the treatment with sulfur dioxide tends to cause the formation of th poly-sulfones. The olefinic hydrocarbons, and particularly the fractions which contain relatively high percentages of diolefins, are quite reactive, and will tend to form organic peroxides even by a mere contact with air at ordinary temperatures and pressures. Therefore, after a hydrocarbon fraction has been treated for the removal or decomposition of the peroxides present therein, it is essential "to prevent any further formation of the organic peroxides in the interim between the purification step and the time when theperoxide-free fraction is reacted with sulfur dioxide under conditions favorable to the formation of the monomeric sulfones of the di- I oleflns present therein. This may be effected by reacting the hydrocarbons with the sulfur dioxide substantially immediately after the removal of the peroxides therefrom, by the addition of inhibitors, such as pyro'gallol, pyrocatechol, or the like, to the purified hydrocarbons, by storage in an inert atmosphere, or by emplbying other known means or methods of inhibiting peroxide formation.

Although the mo] ratio of the sulfur dioxide to the diolefins may vary within relatively wide limits, in order to recover high yields of the desired monomeric sulfones it is preferable to use the sulfur dioxide in amounts greatly in excess of those necessary for the conversion of the dioleflns into the corresponding -mono-sulfones.

For example, other conditions being maintained byincreasing the moi ratio of sulfur dioxide to isoprene from about 2:1 to. about 4:1, it is possible to raise the yield of the isoprene sulfone from about 78% to about 99.5%. This increase in the yield of the mono-sulfones is effected without the use of any catalysts and/or restraining agents, the sole requirement being that the diolefin-containing hydrocarbon fraction be free from organic peroxides. This discovery is contrary to the wellaccepted opinions to the effect that the use of sulfur dioxide in excess of the amount necessary to combine with the acyclic dioleflns tends to form insoluble amorphous addition products (poly-sulfones). Consequently, in order to inhibit the formation of these undesirable by-products, it was heretofore the general practice to avoid the use of large excesses of sulfur dioxide and/or to cause the hydrocarbon mixture to be contacted step-wise with several relatively small amounts or doses of the sulfur dioxide, each of these doses being usually considerably less than one-half of the total weight of the hydrocarbon fraction treated. Such a procedure is generally undesirable because it consumes large periods of time, thereby rendering the process uneconomical. The

- use of peroxide-free oleflns or olefin-containing hydrocarbon fractions allows the use of large excesses of sulfur dioxide without the tendency to form the undesirable poly-sulfones. Such a procedure decreases the overall reaction time and, at the same time, permits the recovery of high yields of the monomeric sulfones of the acyclic diolefins present in the reacting mixture.

In accordance with the present process, it is preferable to effect the addition reaction in the liquid phase, or at least under such conditions of operation that the reactants, namely sulfur'dioxide and the acyclic dioleflns, are predominantly in the liquid state. acyclic diolefins, the reaction temperature should be maintained in the neighborhood of 100 C. However, somewhat higher or lower temperatures may also be used. When the operating tempera- In the case of most of the filtration by suction.

ture drops too low, the addition reaction rate becomes so slow as to render the process uneconomical. On the other hand, care should be taken to prevent the use of excessively high temperatures at which substantial decomposition ofthe sulfones occurs. Also, although the reactants may be at pressures which are only suflicient to maintain them in a liquid state (at the operating temperatures), higher pressures may also be employed. In this connection it must be noted that the reaction pressure is considerably higher than that at which the reactants are introduced into the reaction vessel (e. g. autoclave). This is due to the fact that it is generally preferable to effect this introduction of the reactants at or below ordinary temperatures, whereas the reaction temperature is in the neighborhood of 100 C. As a general rule, the reaction pressures in the autoclave are between about 150 lbs. per

sq. in. and about 200 lbs. per sq. in., or higher,

depending in part on the type of dioleflns treated.

The invention is further illustrated by the following specific examples, it being understood that there is no intention to be limited by any details thereof, sincemany apparent variations may be made.

Example I A freshly distilled, peroxide-free hydrocarbon fraction boiling between 28 C. and 55 C., and produced by thermal cracking of the second cut straight-run gasoline, was employed. This fraction'(which predominated in oleflns having five carbon atoms per molecule) upon analysis was found to contain about 36 weight percent of acyclic diolefins. The hydrocarbon fraction and sulfur dioxide were then separately liquefied by mol of the above hydrocarbon fraction (which closed and placed into boiling water to maintain the reaction temperature within the reactor at between about 99 C. and about 100 C., the pressure within the reactor rising to about 150 to 1'15 lbs. per sq. in. The reaction was continued for aperiod of 2 hours, after which the unreacted gases were released while the liquid fraction (about 0.272 mol) was conveyed to a container which was then cooled to a temperature of about -13 C. This cooling caused the formation of large white crystals which were' separated from the remaining liquid fraction by The crystals, having a melting point of 64 C., were readily soluble in most solvents, and upon analysis showed that they were the crystals of isoprene mono-sulfone. The remaining liq-uid fraction was then found to consist of piperylene mono-sulfone which is believed to have the structural formula cn=cn on, err-cm s or Analyses and determination of the physical contents of a sample of this mono-sulfone gave the followingresults:

1 Found Calculated Density, d-fll/i l. 2220 Refractive index, N-20/D l. 4945 Carbon percent 47. l 45. 5 Hydrogen d0. 6. 41 6. 6 uliur d0. 23.1 '24. 2 Bromine number 122 121 C. and about C. The overhead gaseous fractions were conveyed through alkali scrubbers containing a 10% aqueous solution of sodium hydroxide. This removed the liberated sulfur dioxide. The remaining gases were then condensed, and were found to be substantially pure piperylene and isoprene, respectively.

Example II A freshly distilled, peroxide-free hydrocarbon fraction obtained in the same manner as that used in the previous example,-and having the same percentages of the different monoand diolefins, was reacted with liquid sulfur dioxide under the same conditions as those employed in Example 1, except that the reaction time was shortened to about hour. The total yield of sulfones dropped to about 70%, these sulfones having a greater percentage of isoprene monosulfone.

The unreacted gases were then again treated with. an excess of sulfur dioxide to yield an additional amount of a diolefin sulfone which was found to be practically pure piperylene sulfone. I

- The above examples clearly show that isoprene and piperylene (as well as theirrespective monosulfones) may be separately recovered from hy- I drocarbon mixtures containing the same by subjectlng such mixtures, at superatmospheric pressure and temperatures of about 100 C., to the action of sulfur dioxide (preferably employed in a large excess over the amount necessary to form the mono-sulfones) by cooling the reaction mixture to effect the solidification of the isoprene sulfone, and by separating the same from the normally liquid. piperylene mono-sulfone by any known means, such as filtration, centrifuging. decanting, or the like. If desired, the'respective sulfones may then be decomposed to-yield substantially pure isoprene and piperylene, respectively.

The present process is also applicable to the separation of substantially pure piperylene from hydrocarbon fractions boilingwithin a very narrow boiling range and containing mono-olefins and piperylene as the only diolefin. The following example shows the specific procedure:

Example II I A freshly distilled, peroxide-free hydrocarbon fraction boiling between 41 C. and 44 0., produced by straight distillation of a product formed by crackingsecond'cut straight-run gasoline, was

employed. weight per cent of piperylene.

This fraction contained about 42.8 The formation of the sulfone was eifected accordin to the process described in Example I, the sulfur dioxide being used in a mol ratio of 4:1 and the reaction period being about 2 hours. After removal of the unreacted Products, the piperylene sulfone was obtained in a yield of 96.3%. This mono-sulfone was then decomposed by heating to 125 C.- 130 C. The diolefin fraction thus produced, after separation of the liberated sulfur dioxide, analyzed 99% pure piperylene.

The above examples disclose the use of peroxide-free hydrocarbon fractions. As noted above, the presence of organic peroxides under' by otherwise destroying and/or removing the organic peroxides from the hydrocarbon fracti on to be subjected .to the action of sulfur dioxide.

Although the process is particularly adapted to the separation of isoprene and piperylene from hydrocarbon mixtures containing the same, it also finds utility in the treatment of hydrocarbon fractions containing other acyclic diolefins. For example, it was found that some coniugateddiolefins having six carbon atoms per molecule form normally liquid mono-sulfones, so that they may be thus separated from the othernormally solid sulfones. Instead of separating the sulfones prior to their decomposition, all of the mono-sulfones may be decomposed in toto, and the resulting diolefin fractionmay then be treated, for instance, by careful fractionation .to recover the individual diolefins. If a C fraction contains cyclopentadiene (which apparently does not form the mono-sulfone) it may be advisable to separate this diolefin for instance by the abovedescribed method of polymerization to dicycloactants in the liquid state, recovering the resultant addition products, cooling said addition products to crystallize the isoprene sulfone present ther'ei'n, separating the crystalline isoprene sulfone from the remaining liquid comprising piperylene mono-sulfone, subjecting the isoprene sulfone and the piperylene sulfone to elevated temperatures to eflect their decomposition, and separating sulfur dioxide from the resultant reaction products thereby producing high yields of substantially pure isoprene and piperylene, respectively.

2. The process according to claim 1, wherein the sulfur dioxide employed for the production of the sulfones is .used in a quantity in excess of that necessary to combine with the acyclic diolefins present in the hydrocarbon fraction treated.

3. A process for recovering isoprene and piperylene from hydrocarbon mixtures containing same which comprises contacting a peroxide-free hydrocarbon fraction predominating in olefins having five carbon atoms per molecule and contain-- ingisoprene and piperylene, with sulfur dioxide employed in a quantity in excess of that necessary to combine with said diolefins. subjecting the mixture to an elevated temperature in the neighborhood of 100 C. and to a sup'eratmospheric pressure sufllcient to maintain the reactants in the liquid state for a period of time'suillcient to effect the addition reaction, recovering the resultant addition products, cooling said products to crystallize the isoprene sulfone, separating the remaining liquid comprising piperylene mono-sulfone, and separately decomposing said sulfones to-recover high yields of substantially pureisoprene and piperylene, respectively.

4. The process according to claim 3, wherein the hydrocarbon fraction, substantially immediately prior to the reaction thereof with sulfur dioxide, is subjected to distillation to separate from said-fraction any organic peroxides which may be present therein.

C., under a superatmospheric pressure and for a.

period of time suflicient to effect the addition reaction, separating the resultant addition products, cooling said addition products to crystallize the formed isoprene mono-sulfone, and separating said crystalline isoprene sulfone from the remaining liquid fraction comprising monomeric piperylene sulfone.

6. The process according to claim 5 wherein the addition products obtained from the interaction of the acylic diolefins and sulfur dioxide are cooled to a temperature below about 15 C. to efiect a complete crystallization of the isoprene sulfone present therein.

7. A process for recovering substantially pure piperylene from hydrocarbon mixtures containing said acyclic diolefin, isoprene and other hydrocarbons ofa greater degree of saturation, which comprises subjecting said hydrocarbon mixture to distillation to recover a peroxide-free fraction, reacting said fraction with sulfur dioxide at an elevated temperature and a superatmospheric pressure sufiicient to maintain the reactants in the liquid state, separating the addition products comprising isoprene and piperylene sulfones, cooling said mixture to crystallize isoprene sulfone, separating said crystalline mass from the remaining liquid comprising piperylene sulfone, and decomposing said liquid sulfone to recover substantially pure piperylene.

8. A process for producing and recovering monomeric isoprene and piperylene sulfones which comprises reacting sulfur dioxide with a peroxide-free hydrocarbon fraction containing isoprene, piperylene and other hydrocarbons of a greater degree of saturation, effecting the reactemperature and a superatmospheric pressure toeflect an addition reaction between sulfur dioxide and diolefins, separating the addition products from the unreacted products, cooling said products to substantially room temperature to effect the crystallization of some of the sulfones, and separating the crystalline mass from theremaining liquid fraction comprising monomeric piperylene sulfone.

RUPERT C. MORRIS.

HARRY ma V. FINCH. 

